1

Early Polychrome Glazes on a Chinese Ceramic Bead

of the Warring States Period

Nigel Wood1, Ian C. Freestone

2 and Colleen P. Stapleton

2,3

1Research Laboratory for Archaeology, University of Oxford, Oxford OX1 3QJ, UK and

University of Westminster, Harrow HA1 3TP, UK

2Department of Scientific Research, British Museum, London WC1B 3DG, UK

3Present address: Department of Geology, University of Georgia, Athens, GA 30602, USA

Introduction

Some unusual Chinese ceramic beads, produced in imitation of Western glass eye beads

appear to represent extremely early examples of low temperature glazing. Chinese beads of

this type (Fig. 1) appear to have been excavated from the tomb of the Marquis Yi of Zeng

(5th C, B.C.), which suggests that the technology was well-developed towards the start of

the Warring States period (475-221 B.C.) (Zheng Hou Yi mu 1989, Lu and Hu 1988).

Faience is relatively rare in china, but the polychrome glazed beads which are the subject of

the present paper have a very faience-like appearance. The bodies consist of a hard cream-

white material and are overlain by an opaque white glaze ground over which lie red-brown,

opaque-yellow and cold blue glazes, arranged in a formal geometric design and in high

relief. They appear to emulate glass eye-beads which are considered to have been made in

China at this time, having been shown by many analyses to have characteristic lead oxide -

barium oxide - silica compositions which are rare outside China (Brill et. al. 1991b).

Monochrome faience beads with low-fired glazes are known from the early Western Zhou

period, but have generally been considered imports from the West. Although Brill, Tong

and Zhang (1989) found the interstitial glass of one such bead to be rich in potash,

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consistent with a Chinese origin, a later publication (Brill et al. 1991a) considered the

origin of the bead open. Thus it is possible that beads of the type discussed here represent

the earliest low-fired glaze technology in China and it is highly probable that they are

examples of the earliest indigenous polychrome glazes.

Fig. 1,. Chinese Warring States faience bead with red-brown, yellow, blue and white glazes on a white

glazed ground. L. 20 mm, analysed in the present study.

Fig. 2, Typical Chinese Warring States faience eye beads (top row) and glass eye beads (second and

third rows). (After Yoshimizu,1989). Fig. 2 Omitted from this version

While many examples of Chinese glass beads have been analysed, their relationships with

the contemporary glazed ceramic beads are unclear. In order to explore the technology

used to make these early Chinese beads, and to understand their connections with

contemporary Chinese glass, we have analysed a single Chinese polychrome glazed bead

of the Warring States period. The bead is of interest because both stylistically and

technologically, the glazes appear closely related to those on an earthenware pot of the

Warring States period, reported on by Wood and Freestone 1995. The main techniques

used were scanning electron microscopy and energy dispersive X-ray analysis (SEM),

with X-ray diffraction (XRD) used to confirm the identity of some minerals.

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Results

The bead-body. In the SEM, the pale stony body of the bead proved to have a highly

heterogeneous structure, composed of numerous glass-rich fragments which were sintered

together but had not fully fused and flowed, leaving a high proportion of open pores. These

glass particles are very variable in composition and in some cases have partially devitrified

to crystallites of diopside, feldspar or apatite. The bulk analysis shows about 70% silica,

typical of many clays or glasses but much lower than faience from Western Asia; however,

the body is neither rich in alumina, like a clay, nor rich in alkalis, like a glass; instead it is

rich in alkaline earths and phosphate:

Table 1 Analysis of bulk body of bead

SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O P2O5 MnO

Bulk bead body 69.4 3.5 1.4 7.8 5.7 5.0 1.8 4.7 0.3

Thus, although superficially similar in appearance to the faience of the West, the body of

the bead is not composed of quartz, which is an essential component of faience as normally

defined.

The bead glazes. The glazes on the bead contained many mineral inclusions (often quartz

and albite), suspended in lead oxide- and baria-rich glasses. The angular particle shapes,

coupled with reaction rims on the feldspars, indicate that they are firing relicts of glaze-

batch material, rather than the products of devitrification. The compositions of the four

glaze-colours proved as follows: --

Table 2 B White, blue, yellow and red glazes used on bead

SiO2 TiO2 Al2O3 Fe2O3 CuO CaO MgO K2O Na2O BaO PbO Cl

White 58.4 0.2 4.8 0.5 <0.1 0.7 0.4 1.0 2.6 11.2 19.1 0.8

Blue 49.9 0.9 4.4 0.5 2.4 0.9 0.4 1.2 2.2 14.8 21.9 0.5

Yellow 27.0 0.4 8.6 4.7 <0.1 1.5 0.7 0.7 0.8 20.1 35.0 0.5

Red 42.3 <0.1 2.0 17.8 <0.1 2.2 0.4 0.7 1.1 8.9 24.2 0.5

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In terms of their microstructures, the various glazes showed the following

features: -

The opaque white glaze. Abundant angular fragments of quartz, up to about 0.2 mm

diameter, opacify this glaze, together with a subordinate amount of albite of about the

same size. The glassy matrix has not reached equilibrium and the distribution of lead

is uneven. Low levels of Fe2O3, CaO, MgO and K2O suggest that these are impurities

associated with the major ingredients, rather than conscious additions.

The opaque blue glaze. This glaze also contained many partially reacted quartz and

albite grains. Additionally small crystals, less than 0.005 mm long, were identified as

barium copper silicate, containing about 31% BaO, 15% CuO and 51% SiO2, very

close to the ideal composition of the rare mineral effenbergerite (BaCuSi4O10). The

presence of this mineral was confirmed by XRD analysis. The morphology of the

crystals suggests that they grew from the glaze mixture and are therefore related to

the synthetic version of this mineral, Han blue.1

The opaque red-brown glaze. Quartz grains are present in the red-brown glaze, but are

not as abundant as in the white. The reddish colour of the glaze, and much of its

opacity, comes from angular grains of hematite, up to about 0.07 mm diameter. No

feldspar inclusions were found, and this is reflected in the glaze=s lower alumina

level (1.96%). The glaze is thinly applied, only up to 0.1 mm in the section taken,

compared with 0.3 mm for the yellow.

The opaque yellow glaze. Few grains of quartz are present in this glaze and its opacity

is due mainly to abundant, well-formed crystals of the barium feldspar, celsian,

BaAl2Si2O8 (identified by XRD). The celsian crystals tend to be less than 0.005 mm

long. Most of the iron oxide in this glaze (c. 4.6%) is present in the glassy phase,

presumably as Fe3+

, where it provides a yellow solution colour. Alumina, at 9%, is

comparatively high. Lime and magnesia too (at 1.5% and 0.74% respectively) are

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higher than in the blue and white glazes.

Fig. 3, SEM back-scattered image showing porous bead body overlain by white glaze (containing

angular quartz and albite fragments in a high Pb+Ba glass), overlain by red and yellow (top) glazes

respectively. Feld of view 2.4 mm.

Fig. 4, SEM back-scattered image of yellow glaze showing numerous fine secondary celsian crystals.

Field of view is 0.13 mm across

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Discussion

The bead body. While the body of the bead seems neither glass nor clay its

composition does resemble the ashes of fast-growing plants with tough siliceous

stems, such as rice-straw, fern and sorghum: --

Table 3 Ashes of plants with fast-growing siliceous stems (Ash analyses from Zhang 1986a)

SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O P2O5 MnO

Bulk bead body 69.4 3.5 1.4 7.8 5.7 5.0 1.8 4.7 0.3

Rice-straw ash 75.8 2.1 0.5 5.8 2.6 6.7 1.45 4.7 0.6

Fern ash 70.8 5.5 1.2 8.5 4.0 5.2 0.11 1.2 1.8

Sorghum ash 70.8 5.5 2.5 7.6 3.8 6.0 0.6 1.6 1.8

This raises the possibility that the bead body may have been made entirely from

botanic ash. In particular, the high phosphate content is particularly indicative of a

vegetal ash, as is the heterogeneity of the material and its high fusibility. If the body

was ash, some organic binder or paste may have been used to help form the bead, and

to hold the ash together, which may in part explain its high porosity. The use of a

ceramic body made entirely from plant ash would have been unusual and, on present

evidence, seems to have neither precedents nor descendants in ceramic history.

Advantages of this amorphous material over traditional quartz-based polycrystalline

faience compositions would have been an expansivity more compatible with lead-

baria glazes (Kazmarczyk and Hedges, 1983), as well as improved sintering

behaviour, which produced a harder and tougher body than quartz-based faience.

.

The bead glazes. The coloured surfaces, applied to the bead-body, are true glazes,

albeit somewhat underfired. They have not been fritted before application and some of

their original batch-material can be seen in the SEM pictures. However, the less-than-

complete melting evident in these glazes was probably necessary to preserve the

integrity of the applied and superimposed coloured-glaze patterns and to maintain

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their opacity and colour. Had these glazes been taken to a full melt they would have

merged and run, and lost their definition. This layered approach produced coloured

ornament in much higher relief than contemporary Chinese glass eye-beads, where the

different coloured glasses were levelled by flame-work and/or marvering.

In terms of the glazes’ original compositions, the results suggest the following:

White. The white glaze was made from crushed quartz and albite mixed with lead and

barium minerals. Given the small sample areas analysed, the BaO/(BaO+PbO) ratios

in the white, blue and yellow glazes are relatively constant at 0.36, 0.40 and 0.36,

respectively. Naturally occurring lead-barium minerals are apparently unknown but a

mineral deposit with a relatively constant lead:barium ratio may have been utilised.

The simplest recipe that could have been used for this glaze would have been a

mixture of a crushed quartz-feldspar rock, such as a pegmatite or aplite, with a

crushed lead-barium ore in proportions of about 2: 1. However, a recipe made from

separate additions of quartz, feldspar, a lead mineral and a barium mineral cannot be

ruled out.

Blue. As for white, with an addition of copper. The copper could have been added as

oxidised metal, or as a natural copper mineral. However it may have been added in the

form of prepared Han blue, the tetrasilicate of copper and barium, prepared with a

small amount of lead oxide and which, along with related purple its purple variant,

was often used as a paint pigment in Warring States and Han China (FitzHugh and

Zycherman, 1983, 1992, Herm et al 1995a, Herm et al 1995b). Although the Han blue

found in the glaze seems to have crystallised during firing, it is not impossible that

these crystals developed and grew from dissolved Han blue additions. This possibility

is supported by the slightly higher ratio of barium:lead in the blue glaze, relative to the

yellow and the white (see above), suggesting that a barium-rich but lead-free

compound may have been added.

8

Red. The red seems to be a mixture of crushed quartz with lead and barium minerals,

coloured with a large amount (c. 18%) of hematite powder. However it is not

impossible that the hematite ore itself contained abundant quartz. The low alumina

and soda contents of the red glaze suggest that the source of quartz may not have been

the quartz-feldspar material typical of the blue and white glazes. In addition, the

BaO/(BaO+PbO) ratio is significantly lower than in the other glaze colours, at 0.27.

Thus the raw materials for the lead and silica of the red may have differed from those

of the other glazes

Yellow. The absence of crushed quartz and albite, together with higher levels of

alumina, lime and magnesia in this glaze, suggest that its iron content may have been

supplied by a fusible ferruginous clay. Indeed a mixture of a red clay with a lead-

barium ore, in about 1:1 proportions, would explain both the chemistry and the

microstructure of this glaze. The above-average alumina level (8.58% Al2O3) may

have encouraged the growth of celsian during firing, which has rendered the yellow

glaze somewhat opaque. This distinguishes the yellow glaze from true Chinese lead-

baria glass where the usual opacifier is barium disilicate B Chinese glass being too

low in alumina to generate barium feldspar (Brill et al 1991).

The high PbO+BaO total (55.1%) in the yellow glaze would have helped to create a

solution colour from the iron present in the glaze, and the glaze is visibly more fusible

than the white, the blue and the red. This may explain why it was used as a topmost

detail on the bead as it unlikely that it could have supported applied glazes without

dissolving them. Of all the glazes on the bead, its composition is closest to later Han

lead glazes, such as an example of an Eastern Han green glaze on a vessel in the

Victoria and Albert Museum, London (Wood et al 1992):

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Table 4 Warring States yellow bead-glaze and Eastern Han green lead glaze compared

SiO2 TiO2 Al2O3 Fe2O3 CuO CaO MgO K2O Na2O BaO PbO SO3 Cl

Bead yellow 27.0 0.4 8.6 4.7 <0.1 1.5 0.7 0.7 0.8 20.1 35.0 <0.1 0.47

Han Green 33.4 0.6 3.9 2.0 3.0 2.0 0.7 0.5 0.4 7.7 43.5 0.6 -.-

It has been suggested that the Eastern Han green glaze containing baria could have

been made from a mixture of sandy loess with lead and barium ores, and coloured by

a copper-tin mixture, perhaps oxidised bronze (ibid, 1992). Replications of this Han

green glaze matured just above 1000oC and from this we might propose a firing

temperature for the bead somewhere between 1000o and 1050

oC.

The similarity of the Han green glaze to the bead yellow glaze of the bead may

suggest that Han lead glaze technology owed something to the compositional

approaches developed and adopted for making the more fusible and translucent types

of bead-glazes in the Warring States period.

Relationship to Chinese glass. The analyses show that these glazes are not quite the

same as the glasses used in contemporary Chinese glass beads, although there are

some interesting parallels.

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Table 4 Analyses of Chinese glass beads (5th-1st C. BC) (1-4 from Shi et al, 1991; 5-7 from

An Jiayao 1996)

SiO2 TiO2 Al2O3 Fe2O3 CuO CaO MgO K2O Na2O BaO PbO

1. Blue bead 41.4 0.01 0.89 0.27 2.07 1.37 0.16 0.16 5.94 9.7 37.4

2. Black bead 37.3 0.05 1.19 7.35 0.42 1.89 0.61 0.37 3.75 9.4 37.5

3. Colourless bead 51.3 0.01 0.46 0.1 0.01 0.37 1.5 0.08 6.12 11.4 28.3

4. Blue bead 52.4 0.03 1.21 0.28 1.31 1.48 2.62 0.16 10.1 11.1 19.2

5. Glass eye bead 43.41 - 4.80 0.14 - 0.69 - 0.27 7.28 14.37 26.88

6. Glass eye bead 37.56 - 4.95 0.49 - 1.75 1.41 - 4.47 16.07 32.00

7. Glass eye bead 36.53 - 7.36 0.25 - 1.69 0.39 - 4.73 15.49 31.53

Both Warring States bead-glasses and Warring States bead-glazes are lead-barium

silicates with sodium oxide present as a supplementary flux. However the glass bead analyses

are noticeably higher in soda than the glazes, and commonly lower in alumina. SEM analysis

shows that most of the alumina and sodium oxide present in the white and blue glazes is in the

form of the insoluble material albite, which has a theoretical Na2O content of 11.8% and an

Al2O3 content of 19.4%. By contrast the glasses in rows 1-4 of Table 4 have sodium oxide

contents that are from twice to nine times their alumina levels. Such high soda and low

alumina levels in the glasses could not have been supplied by albite and must therefore

represent the use of some soluble sources of sodium oxide in the original glass batches.

An apparently unusual group of glasses which are very similar to the bead glazes are

shown in rows 5-7. These are analyses of eye-beads from Guweicun Tomb 1, Huixian,

Henan, presented by An Jiayao (1996) and dated to the Middle and Late Warring States

Period. They not only have high alumina like the bead glazes but also their barium/lead

ratios are very similar, with BaO/(BaO+PbO) of about 0.34. Thus these glasses were

made from very similar materials and recipes to the bead glazes, perhaps in the same

locality. The main differences are in the soda contents of the glasses, which are double

those in the glazes. It would appear that addition of a few percent soda to the bead glazes,

perhaps with a higher firing temperature, would have produced a workable glass. The

glazes may represent an underfired intermediate material from the glass making process.

Glass-batch production copes easily with soluble materials, but insoluble ingredients in

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glazes are a great advantage. While glazes can be fritted to overcome material solubility,

there seems some benefit in the use of unfritted glazes in the case of the glazed bead

technology, as unmelted batch material encouraged opacity in the fired glazes, and

supplied a useful stability in firing.

Warring States glazed vessels. Perhaps the best parallels to the glazed-bead technology

described above can be seen in the small group (four known examples) of Warring States

pottery vessels, decorated with red-brown, yellow, blue and white glazes and bearing

patterns closely related to those seen on the Chinese faience beads. The authors studied

one highly weathered example in the British Museum’s collection, semi-quantitatively in

1995 (Wood and Freestone, 1995). As with the bead glazes, lead oxide and baria were the

main fluxes, and the glaze-colours were yellow and red from ferric oxide, and blue from

effenbergerite. The vessel’s body, however, was thrown from ordinary gritty red

earthenware clay.

Fig. 5. Chinese Warring States pottery jar with lead-baria coloured glazes.

Height 9.5 cm. OA 1968 4-22.18. British Museum Photograph by Tony

Milton.

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Conclusion

Both real glass and glazed faience beads were imported from the west into China

during China’s Bronze Age (Zhang et al 1986). These artefacts represented

sophisticated Near Eastern glaze and glass technologies that exploited such silicate-

colours as cuprite-red, cobalt blue, copper-turquoise, calcium antimonite white and

lead antimonate yellow (Kaczmarczyk and Hedges 1983, Bimson and Freestone 1987,

Lilyquist and Brill 1993). These colours were often combined to create colourful ‘eye-

beads’, manufactured across the Near East, the eastern Mediterranean, and at some

sites in Western Asia (Yoshimizu 1989).

In China two technologies were employed to imitate these imports: true lead-barium

glasses, and lead-barium glazed ceramic beads. Our analyses of one example of the

latter type have shown an apparently unparalleled body-type made entirely from fused

plant ash, and ceramic glazes made from crushed siliceous materials, combined with

lead and barium oxides. The bright colours of the Western beads were copied on this

glazed ceramic beads of this type with a more subdued palette that included an iron-

yellow, an iron-red and a copper-barium-silicate blue.

The faience-bead glazes differ from contemporary Chinese glasses in some important

respects, most notably in their use of insoluble and unfritted ingredients. In some

cases these various glaze colours were superimposed in four layers - an effect made

possible by good glaze-viscosity and moderate underfiring. This unusual technology

seems to have been extended to include the production of small group of glazed

thrown vessels, although in this case the ash-based body was replaced with ordinary

earthenware clay (Wood and Freestone, 1995).

Taken together, the glazed bead and the decorated pottery vessel seem to show the

earliest use of low-fired glazes in China, the first use of copper as a glaze colourant in

China, the first use of iron-red and iron-yellow glazes in China, and the first use of

13

polychrome glaze-decoration in Chinese ceramics. In their manipulation of colour,

base-glaze composition and glaze-viscosity they represent a more complicated and

sophisticated technology than that used for contemporary clay-and-ash stoneware

glazes in southern China (Zhang 1986b). Nonetheless, the making of glazed-faience in

China ended in the late first millennium B.C., and it was not until lead-based

overglaze enamels were developed in China in the late 12th century AD that certain

aspects of this technology were rediscovered, particularly the use of the iron-red

earthenware glaze. Use of the effenbergerite-blue in Chinese glazes, however, seems

to have been restricted to the early period, and was not revived.

As to the larger question of how such an unusual and distinctive approach to glass-

and glaze making arose in China in the Warring States period, this remains a problem.

The importance of lead in these technologies may suggest some connection with

metallurgy, but pigment-production may have been another route to lead-rich glasses

and glazes. At present a proper chronology for glass, glazed faience and barium-

copper-silicate pigment technologies is lacking for China, but this aspect of the

subject should become clearer with further excavations and investigations.

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